Denali National Park & Preserve Air Quality Information
Overview
Because of Alaska’s low population density and relatively low level of industrial activity, air pollution emissions are low and air quality in Denali NP is generally very good. However, since the background air quality is relatively clean, even low levels of pollutants can have a noticeable impact on the park’s air. Emissions from industrial and mobile sources, both regional and international, can cause haze and degrade air quality. International transport pathways bring low concentrations of airborne contaminants into the park from Europe and Asia across the Arctic and Pacific Oceans. Among these contaminants are sulfur and nitrogen compounds, toxic heavy metals, and pesticides, originating from sources as diverse as power plants, smelters, agriculture, and residential activities. These pollutants are eventually deposited onto the snow, water, vegetation, and soils of Denali NP. In addition to anthropogenic contaminants, naturally-occurring wildfire smoke causes haze in the park, from fires in Alaska and as far away as Canada and Russia.
Air quality related values (AQRVs) are defined as those resources that are potentially sensitive to air pollution, including visibility, water quality, soils, vegetation, and wildlife. Visibility is a very sensitive AQRV in Denali NP. Because the air is generally so clean in the park, just a small amount of pollutant particles can cause a noticeable haze. The U.S. Environmental Protection Agency’s (EPA) Regional Haze regulations require states to establish goals for each Class I air quality area to improve visibility on the haziest days and ensure that no degradation occurs on the clearest days. As part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, aerosols are monitored at Denali NP to calculate and track visibility trends (1988 to present). Summer visibility was directly measured from 1988 to 1994, using an automated 35mm camera. In addition, IMPROVE aerosol monitoring is conducted at Trapper Creek, about 36 km south of the park boundary (2001-present). Data indicate that visibility in the park is sometimes impaired by human-caused pollution.
Denali NP has remarkable water resources, including large rivers, lakes, and countless streams and wetlands. Many of these waters receive glacial runoff, rich in base cations. As a result, these may be well buffered from the effects of atmospheric pollutants like nitrogen and sulfur compounds that can cause acidification. Other aquatic environments may be sensitive to airborne contaminant inputs, but not well studied in the expansive, roadless areas of the park.
Estimates of total atmospheric deposition of sulfur and nitrogen compounds can be made by adding wet and dry deposition. Wet deposition has been monitored in Denali NP since 1980 as part of the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). The site ID is AK03. In order to estimate dry deposition, weekly concentrations of sulfur and nitrogen compounds have been measured at Denali NP (site DEN417) since 1998 as part of the Clean Air Status and Trends Networks (CASTNet). Total nitrogen and sulfur deposition rates for the park are low. CASTNet sites also operated at Poker Flat Research Range (north of the park) from 1998 to 2004, and at Trapper Creek from1998 to 2001.
In addition to pollutants like nitrogen and sulfur compounds, atmospheric deposition of toxic and persistent contaminants from international transport may affect Denali NP aquatic and terrestrial resources and the wildlife that depend on them. Many of these chemicals bioaccumulate in ecosystems, reaching unhealthy levels in organisms high on the food chain.
Sediment cores from Wonder Lake were analyzed as part of the Arctic Contaminants Research Project. Anthropogenic contaminants, including polycyclic aromatic hydrocarbons, dioxins, dibenzoburans, and polychlorinated biphenyls (PCBs), were found in the sediment samples. Concentrations of PCBs, while low compared to levels found in more industrialized regions, were the highest of any remote arctic or subarctic lake surveyed throughout the circumpolar north, in a synthesis conducted by the Arctic Monitoring and Assessment Programme.
The NPS Western Airborne Contaminants Assessment Project (WACAP) is currently evaluating water, snow, sediments, willow bark, fish, and moose tissue in a number of western U.S. and Alaska national parks, including Denali NP, for the presence of metals (including mercury) and organic compounds.
Several plant species that occur in Denali NP, including Salix scouleriana (Scouler’s willow) and Populus tremuloides (quaking aspen) are known to be sensitive to tropospheric (ground level) ozone. Ozone has been monitored with a continuous analyzer from 1987- present in the park; in 1995, a passive ozone sampler was also used. Trend data from 1990-1999 indicate that ozone is increasing in the park. However, ozone concentrations and doses are well below levels known to cause injury to vegetation.
UV-B radiation has been monitored in Denali NP since 1997 as part of the EPA’s UV-B Monitoring Program. As stratospheric (upper atmosphere) ozone levels decline because of ozone-depleting chemicals, increases in UV exposure are possible. Increased exposure to ultraviolet radiation has negative implications for human health and plant productivity.
Additional information on in-park emissions at Denali NP is available in 2002 Air Emissions Inventory-Denali National Park and Preserve (November 2003).